A hot stick is an insulated pole, typically made of fiberglass, used by electric utility workers (linemen) when working on energized high-voltage electric power lines to protect them from electric shock. Depending on the tool attached to the end of the hot stick, it is possible to test for voltage, tighten nuts and bolts, apply tie wires to insulators, open and close switches, replace fuses, lay insulating covers on wires, and perform various other tasks while not exposing the crew to a large risk of electric shock. The hot stick may be up to 30 feet long. In the United States, ASTM Standard F 711 specifies the stringent requirements for hot sticks.
One of the tools attachable to the end of a hot stick is a hook that is inserted into a hole of a structure to grab the structure. It would be convenient for the hole to always be oriented vertical to the ground so that the lineman can easily insert the hook into the hole. For fuse holders and other fixed structures having a grasping hole, the hole is typically vertical to the ground. However, some insulating structures developed and sold by the present inventor use one or more removable pins, having grasping holes, for retaining the insulating structure in place. The pins (and grasping holes) are arbitrarily rotatable, making it more difficult for the lineman to insert the hot stick hook into the hole for removal of the pins.
Additionally, it is important that the pins remain securely inserted through the insulating structure for retaining it, even during the fiercest storm. Therefore, the prior art retaining pins are designed with a resilient expansion nose portion, where the nose portion partially collapses when being pushed through a hole in the insulating structure and expands after it is completely pushed through. The pin's insertion and removable force is the same. It would be desirable, however, for the pin to be inserted at a lower force for ease of insertion using the hot stick, yet require more force for removal to improve reliability. It is easier to pull with a hot stick than to push.
FIGS. 1-3 describe an insulating structure disclosed in the present inventor's published US Application 2010/0218988 that uses pins to secure the insulating structure in place on a tower. US Application 2010/0218988 is incorporated herein by reference.
Prior art FIG. 1 illustrates the top portion of a steel tower 10 supporting wires 12 carrying high voltages, such as greater than 10 kV. Other structures include those formed of cement or wood. The voltage is typically 3-phase, and at least three wires are supported. The tower 10 is grounded by being imbedded in the ground.
Ceramic insulators 14 support the wires 12, where the minimum distance between any wire 12 and the tower 10, or between any two wires, is determined by the IEEE National Electric Safety Code.
Insulating guards 20 are affixed over the grounded struts 16/18 of the tower 10 to prevent flashover due to a large a bird getting between a strut 16/18 and an overhead wire 12. The guard 20 prevents flashover, since any flashover must travel around the outer surface of the guard 20 to the grounded structure. This is because the dielectric strength of the guard 20 material is many times that of air, and the air around the guard 20 will break down before the guard 20 material will break down.
Pins 24 retain the guard 20 in place by blocking the guard 20 from being lifted off the strut 16/18 by the wind.
FIG. 2 is a perspective view of a single guard 20. The guard 20 is formed of a sheet of one-eighth inch thick HDPE (a plastic) that is cut and bent in the shape shown using conventional techniques.
An angled section 22 is about 3 feet long and wide enough (e.g., 3.25 inches) to fit over a strut 16. Its sides may be about 6-8 inches to completely cover the sides of the strut 16 and still allow room below the strut 16 for passing the retaining pins 24 (FIG. 3) through a round hole in the sides to prevent the guard 20 from blowing off in a high wind. The guard 20 also includes a bottom section 26 that resides over the insulator 14 and a wide middle section 28 that deters a large bird from perching on it.
FIG. 3 is a side view of the plastic retaining pin 24 that is easily inserted through round holes on both sides of the guard 20 after the lineman positions the guard 20 over the upper portion of the angled strut 16 while the lineman is supported on the center body of the tower 10 or in a bucket far from the wires 12. The pin 24 may be 4-5 inches long for use with the guard 20. The body of the pin 24 that is passed through the hole has a circular cross-section. The nose 25 of the pin 24 has a circular bump 29 that contacts the wall of the hole and compresses the nose 25 until the pin 24 is pushed completely through the hole. The contact edge of the bump 29 provides a maximum angle of about 30-45 degrees with respect to the edge of the hole. The length of the bump 26 that must be overcome by pushing the pin 24 is only about one-eighth inch long. The insertion and removal force are the same and about three pounds.
A grasping hole 27 on the pin 24 enables the lineman to grasp the pin 24 using a hook at the end of a hot stick. The pin 24 can freely rotate in the round hole in the guard 20, so the grasping hole 27 will typically not be vertical to the ground when the pin 24 may be later removed. This complicates the removal process.
The same pin 24, of various lengths, is used for the same purpose in a variety of other insulating products to retain the products in place over a wire, insulator connector, metal strut, or other conductor.
What is needed is a retaining pin for an insulator for high voltage applications that is easier to insert yet more difficult to remove, and where the pin's grasping hole remains vertical to the ground for ease of removal and insertion by a hot stick.